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    <title>ShellCheck: SC2070 – `-n` doesn't work with unquoted arguments. Quote or use `[[ ]]`.</title>
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    <h1>SC2070 – ShellCheck Wiki</h1>
    <a href="https://github.com/koalaman/shellcheck/wiki/SC2070">See this page on GitHub</a>
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    <h2
id="-n-doesnt-work-with-unquoted-arguments-quote-or-use--"><code>-n</code>
doesn't work with unquoted arguments. Quote or use
<code>[[ ]]</code>.</h2>
<h3 id="problematic-code">Problematic code:</h3>
<div class="sourceCode" id="cb1"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb1-1"><a href="SC2070.html#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="cf">if</span> <span class="bu">[</span> <span class="ot">-n</span> <span class="va">$var</span> <span class="bu">]</span></span>
<span id="cb1-2"><a href="SC2070.html#cb1-2" aria-hidden="true" tabindex="-1"></a><span class="cf">then</span></span>
<span id="cb1-3"><a href="SC2070.html#cb1-3" aria-hidden="true" tabindex="-1"></a>  <span class="bu">echo</span> <span class="st">&quot;var has a value&quot;</span></span>
<span id="cb1-4"><a href="SC2070.html#cb1-4" aria-hidden="true" tabindex="-1"></a><span class="cf">else</span></span>
<span id="cb1-5"><a href="SC2070.html#cb1-5" aria-hidden="true" tabindex="-1"></a>  <span class="bu">echo</span> <span class="st">&quot;var is empty&quot;</span></span>
<span id="cb1-6"><a href="SC2070.html#cb1-6" aria-hidden="true" tabindex="-1"></a><span class="cf">fi</span></span></code></pre></div>
<h3 id="correct-code">Correct code:</h3>
<p>In POSIX:</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb2-1"><a href="SC2070.html#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="cf">if</span> <span class="bu">[</span> <span class="ot">-n</span> <span class="st">&quot;</span><span class="va">$var</span><span class="st">&quot;</span> <span class="bu">]</span></span>
<span id="cb2-2"><a href="SC2070.html#cb2-2" aria-hidden="true" tabindex="-1"></a><span class="cf">then</span></span>
<span id="cb2-3"><a href="SC2070.html#cb2-3" aria-hidden="true" tabindex="-1"></a>  <span class="bu">echo</span> <span class="st">&quot;var has a value&quot;</span></span>
<span id="cb2-4"><a href="SC2070.html#cb2-4" aria-hidden="true" tabindex="-1"></a><span class="cf">else</span></span>
<span id="cb2-5"><a href="SC2070.html#cb2-5" aria-hidden="true" tabindex="-1"></a>  <span class="bu">echo</span> <span class="st">&quot;var is empty&quot;</span></span>
<span id="cb2-6"><a href="SC2070.html#cb2-6" aria-hidden="true" tabindex="-1"></a><span class="cf">fi</span></span></code></pre></div>
<p>In bash/ksh:</p>
<div class="sourceCode" id="cb3"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb3-1"><a href="SC2070.html#cb3-1" aria-hidden="true" tabindex="-1"></a><span class="cf">if</span> <span class="kw">[[</span> <span class="ot">-n</span> <span class="va">$var</span> <span class="kw">]]</span></span>
<span id="cb3-2"><a href="SC2070.html#cb3-2" aria-hidden="true" tabindex="-1"></a><span class="cf">then</span></span>
<span id="cb3-3"><a href="SC2070.html#cb3-3" aria-hidden="true" tabindex="-1"></a>  <span class="bu">echo</span> <span class="st">&quot;var has a value&quot;</span></span>
<span id="cb3-4"><a href="SC2070.html#cb3-4" aria-hidden="true" tabindex="-1"></a><span class="cf">else</span></span>
<span id="cb3-5"><a href="SC2070.html#cb3-5" aria-hidden="true" tabindex="-1"></a>  <span class="bu">echo</span> <span class="st">&quot;var is empty&quot;</span></span>
<span id="cb3-6"><a href="SC2070.html#cb3-6" aria-hidden="true" tabindex="-1"></a><span class="cf">fi</span></span></code></pre></div>
<h3 id="rationale">Rationale:</h3>
<p>When <code>$var</code> is unquoted, a blank value will cause it to
wordsplit and disappear. If <code>$var</code> is empty, these two
statements are identical:</p>
<div class="sourceCode" id="cb4"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb4-1"><a href="SC2070.html#cb4-1" aria-hidden="true" tabindex="-1"></a><span class="bu">[</span> <span class="ot">-n</span> <span class="va">$var</span> <span class="bu">]</span></span>
<span id="cb4-2"><a href="SC2070.html#cb4-2" aria-hidden="true" tabindex="-1"></a><span class="bu">[</span> <span class="ot">-n</span> <span class="bu">]</span></span></code></pre></div>
<p><code>[ string ]</code> is shorthand for testing if a string is
empty. This is still true if <code>string</code> happens to be
<code>-n</code>. <code>[ -n ]</code> is therefore true, and by extension
so is <code>[ -n $var ]</code>.</p>
<p>To fix this, either quote the variable, or (if your shell supports
it) use <code>[[ -n $var ]]</code> which generally has fewer caveats
than <code>[</code>.</p>
<h3 id="exceptions">Exceptions:</h3>
<p>None</p>
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